Described herein are diketopyrrolopyrrole (DPP) copolymers such as small molecules, oligomers, and semiconducting copolymers based thereon. These molecules may find application in semiconductor layers of electronic devices such as organic thin film transistors (OTFTs) and in organic photovoltaics (solar cells).
Thin film transistors (TFTs) are basic components of many electronic devices, including sensors, image scanners, and electronic display devices. OTFTs offer advantages over conventional, silicon-based materials in that manufacturing costs can be reduced as well as providing mechanical properties such as the devices being physically compact, lightweight, and flexible. OTFTs are generally composed of a supporting substrate, three electrically conductive electrodes (gate, source and drain electrodes), a channel semiconductor layer, and an electrically insulating gate dielectric layer separating the gate electrode from the source and drain electrodes. The channel semiconductor is in turn in contact with the source and drain electrodes. The materials used to make the OTFTs, and the interfacial properties between various layers of semiconductor, dielectric, and electrodes can all affect the performance of the OTFTs.
DPP copolymers are high mobility p-type semiconductors which have been used for thin film transistors. However, due to the relatively high HOMO (highest occupied molecular orbital) energy level of these materials, most of them are sensitive to oxygen and therefore not suitable for fabrication of devices under ambient conditions.
For most semiconductors, if their HOMO level is not well matched with the work function of the electrode material, a significantly lower mobility is often observed in bottom contact devices due to a larger charge injection barrier.
Thieno[3,2-b]thiophene-based copolymers have shown high charge carrier mobility of 0.2-0.6 cm2/Vs (see, for example, McCulloch, I., et al. Nat. Mater. 5, 328 (2006)). However, these copolymers have shown some sensitivity towards oxygen and moisture in air, thus hampering their solution fabrication of TFTs in ambient conditions.
U.S. Pat. No. 7,910,684, incorporated herein by reference in its entirety, discloses a thin film transistor device comprising: a semiconductor layer, the semiconductor layer comprising a compound comprising a chemical structure represented by:
wherein each R is independently selected from hydrogen, an optionally substituted hydrocarbon, and a hetero-containing group; each Ar is independently selected from optionally substituted heteroaryl groups; each M is a conjugated moiety selected from:
and substituted derivatives and combinations thereof; a represents a number that is at least 1; b represents a number from 1 to 20; and n represents a number that is at least 1.
U.S. Pat. No. 7,932,344, incorporated herein by reference in its entirety, discloses a copolymer comprising a structure represented by:
wherein each R is independently selected from hydrogen, an optionally substituted hydrocarbon, and a hetero-containing group; each M is a conjugated moiety selected from:
and substituted derivatives and combinations thereof; a represents a number that is at least 1; b represents a number from 1 to 20; n represents a number from 2 to 5,000; each X is independently selected from S, Se, O, and NR″, where each R″ is independently selected from hydrogen, an optionally substituted hydrocarbon, and a hetero-containing group; each Z is independently one of an optionally substituted hydrocarbon, a hetero-containing group, and a halogen; d represents a number which is at least 1; and e represents a number from zero to 2.
U.S. Patent Application Publication No. 2011/0215,313, and Huo, Lijun, et al. Macromolecules. 42, 6564-6571 (2009), both incorporated herein by reference in their entireties, disclose DPP copolymers in organic photovoltaic devices.
There is a need for materials and methods that will improve air stability of the semiconductor layer while providing high charge carrier mobility.